Lichtenstein M, Guo W, Tartakoff A M
Hebrew University, Jerusalem, Israel.
Traffic. 2001 Apr;2(4):261-7. doi: 10.1034/j.1600-0854.2001.1o002.x.
mRNA export is mediated by RNA-binding proteins which shuttle between the nucleus and cytoplasm. Using an in vitro unidirectional export assay, we observe that the shuttling mRNA-binding protein, hnRNP A1, is exported only extremely slowly unless incubations are supplemented with snRNA-specific oligonucleotides which inhibit splicing. In vivo microinjection experiments support this conclusion. Like many examples of nucleocytoplasmic transport, export of hnRNP A1 requires energy and is sensitive to the presence of wheat germ agglutinin. It does not, however, require supplementation with cytoplasmic proteins. Although the exportin, Crm1, is needed for export of several varieties of RNA, both the in vitro assay and in vivo assays show that it is not required for export of hnRNP A1. In vitro and in vivo studies also show that inhibition of transcription allows continued shuttling of hnRNP A1 and in fact accelerates its export. Judging from the stimulatory effects of targeted destruction of snRNAs, this is likely to reflect completion of the covalent maturation of the RNAs with which hnRNP A1 associates. These observations therefore provide a simple explanation of why multiple RNA-binding proteins relocate to the cytoplasm upon inhibition of transcription in vivo.
mRNA的输出由在细胞核和细胞质之间穿梭的RNA结合蛋白介导。通过体外单向输出试验，我们观察到穿梭的mRNA结合蛋白hnRNP A1输出极其缓慢，除非在孵育时添加抑制剪接的snRNA特异性寡核苷酸。体内显微注射实验支持这一结论。与许多核质运输的例子一样，hnRNP A1的输出需要能量，并且对麦胚凝集素的存在敏感。然而，它不需要补充细胞质蛋白。尽管输出蛋白Crm1是几种RNA输出所必需的，但体外试验和体内试验均表明，hnRNP A1的输出不需要它。体外和体内研究还表明，转录抑制可使hnRNP A1持续穿梭，实际上还会加速其输出。从靶向破坏snRNA的刺激作用判断，这可能反映了与hnRNP A1结合的RNA共价成熟的完成。因此，这些观察结果为体内转录抑制后多种RNA结合蛋白重新定位于细胞质提供了一个简单的解释。
